Article: Petrified stems bearing Dicroidium leaves from the Triassic of Antarctica

Anatomically preserved one to five year-old stems are described from a Triassic site in the central Transantarctic Mountains. They are assigned to Kykloxylon fremouwensis gen. et sp. nov. and are regarded as related to the corystosperm stem Rhexoxylon on the basis of wood and pith anatomy and leaf trace organization. Kykloxylon axes possess a solid vascular cylinder of secondary xylem of the Dadoxylon type, but lack centripetal wood and a narrow pith. The bases of leaves attached to one-year-old stems of K. fremouwensis are similar to the leaves of Dicroidium fremouwensis described from the same locality in Antarctica. The 'Dicroidium/Kykloxylon plant' from Antarctica is branched and more complex than the hypothetical ' Dicroidium /Rhexoxylon plant' reconstructed from disarticulated remains from the Ischigualasto Formation of Argentina. It is suggested that the ' Dicroidium /Rhexoxylon plant' may have been dominant in western Gondwana, whereas the Dicroidium plants with Kykloxylon stems might have had a wider geographical distribution in Gondwana.